The Next Generation Network (NGN) is a service integrated network which takes a packet network as its bearer network to provide a plurality of services, such as fixed phone and mobile phone voice, data, and video. Media Gateway Controller (MGC) and Media Gateway (MG) are two key components of a packet network. The MG functions as service bearer, that is, transforms media of different access manners into the media suitable to be transmitted in an Internet Protocol (IP) network, for example, a Real-time Transport Protocol (RTP)/Real-time Transport Control Protocol (RTCP) flow, while the MGC functions as call control, by which the separation of call control plane and service bearer plane may be implemented so as to share network resources substantially, simplify device upgrade and service extension, and greatly decrease the cost of development and maintenance.
FIG. 1 is a schematic drawing illustrating one common networking of MG and MGC in the prior art. The Media Gateway Control Protocol is the main protocol for the communication between MG and MGC, as shown in FIG. 1, there are two protocols widely employed: Gateway Control Protocol (GCP), for example, H.248/MeGaCo, and Media Gateway Control Protocol (MGCP). Take the H.248 Protocol as an example, various resources in an MG may be denoted by Terminations abstractly. Terminations are divided into Physical Termination and Ephemeral Termination. The former represents some semi-permanent physical entities, such as a Time Division Multiplex (TDM) channel, while the latter represents some public resources applied when used and released after being used, e.g. an RTP flow. The combination of Terminations is denoted by Context abstractly. The Context may include a plurality of Terminations, and therefore the relationship among a plurality of Terminations in a Context may be represented by Topology. The Termination not associated with other Terminations is included in a special Context called Null Context. The MG establishes and releases a Context according to a command from the MGC. A Context is established when a first Termination is added to the Context and released when the last Termination is deleted from the Context.
According to the abstract model of the protocol, call connecting is actually a series of operations on Terminations and Contexts. Such operations are performed through exchanging request and response commands between MGC and MG. The types of command include Add, Modify, Subtract, Move, AuditValue, AuditCapabilities, Notify and ServiceChange. Command parameters, also called Descriptor, are classified into Property, Signal, Event and Statistic. The service-related parameters are converged into a Package logically, and the MGCP, through the Package, permits a Termination to have optional Property, Event, Signal and Statistic so as to support Terminations with various characters.
The Add command is used by the MGC to instruct the MG to add a Termination to one Context; one Context will be established when a first termination is added to the Context by using the Add command. The Modify command is used by the MGC to instruct the MG to modify Property, Event and Signal of a Termination. The Subtract command is used by the MGC to instruct the MG to release the connection between a Termination and the Context in which the Termination is located, and in turn, the statistic information related to the Termination is returned by the MG; it means that one Context is deleted when the relationship between the last Termination and the Context is released. The Move command is used by the MGC to instruct the MG to move one Termination from the Context in which the Termination is currently located to another Context; however the Move command can not move one Termination from the Null Context, and can not move one Termination to the Null Context. The AuditValue command is used by the MGC to request the MG for the current value of Property, Signal, Event and Statistic, which are, in turn, returned by the MG to the MGC. The AuditCapabilities command is used by an MGC to request the MG for all the possible values supported by the Termination about the Property, Signal, Event and Statistic, which are in turn returned by the MG to the MGC. The MG may use the Notify command to notify the event occurred in the MG. The ServiceChange command permits the MG to notify the MGC that a Termination or Termination group will be out of a service or restore a service, permits the MGC to indicate a Termination or Termination group that shall be out of a service or restore the service, permits the MG to notify the MGC that the capabilities of the Termination or Termination group have changed, and permits the MGC to hand over the control for the MG to another MGC; where t. The ID parameter of the Termination specifies the Termination which shall be out of a service or restore the service, and the command will act on the entire MG if the Termination ID of Root is adopted.
According to the definition of the ServiceState Property of the TerminationState Descriptor in the H.248 Protocol, the Termination may be in one of the following three service sates: InService, OutOfService and Test. The InService state denotes that the Termination may be used or is being used for normal communication; the OutOfService state denotes that the Termination can not be used for communication; the Test state denotes that the Termination is in Test. The switching between the service states of a Termination is performed by the ServiceChange command (the Termination is switched to the Test state by the Modify command).
There are a series of parameters in the ServiceChange command, e.g. Method, Reason and Delay. The Method parameter may have the values such as Graceful, Forced, Restart, Disconnected, Handoff and Failover. The Graceful indicates that the entire MG or a termination thereof will be out of service after a specific delay; the Forced indicates that the entire MG or a Termination thereof is out of service accidentally; the Restart indicates that the entire MG or a Termination thereof restore the service after a specific delay; the Disconnected indicates that the MG loses the communication with an MGC but restores the communication with the same MGC subsequently; the Handoff indicates that an MGC hands over the control of an MG to another MGC; the Failover indicates that the standby MG will act when the primary MG is disabled, or the MG detects that the primary MGC is disabled and therefore resorts to the control by the standby MGC. The Reason parameter provides further description for the above Method parameter, while the Delay parameter provides the specific delay for the above Method parameter, and other parameters will not be described in detail here.
It can be seen from the above that the service state of a Termination in the MG may be switched by using the ServiceChange command. For example, the MG or MGC can switch the service state of the entire MG or a Termination in the MG to the InService state using the Restart mode of the ServiceChange command; the MG or MGC can switch the service state of the entire MG or a Termination in the MG to the OutOfService state using the Graceful method or the Force method of the ServiceChange command; in addition, the MG; using the Disconnected method of the ServiceChange command, and the MGC and MG, using the Handoff method of ServiceChange command in coordination, may switch the service state of the Termination to the InService state.